function [b,a] = imp_invr(c,d,T)
% Impulse Invariance Transformation from Analog to Digital Filter
% ---------------------------------------------------------------
% [b,a] = imp_invr(c,d,T)
%  b = Numerator polynomial in z^(-1) of the digital filter
%  a = Denominator polynomial in z^(-1) of the digital filter
%  c = Numerator polynomial in s of the analog filter
%  d = Denominator polynomial in s of the analog filter
%  T = Sampling (transformation) parameter
%
[R,p,k] = residue(c,d);
p = exp(p*T);
[b,a] = residuez(R,p,k);
b = real(b'); a = real(a');